Distance measuring device

ABSTRACT

In a travel measuring instrument ( 10 ), a magnet ( 11 ) which is polarized in the movement direction (R) is disposed against a flux conducting part ( 12 ). The flux conducting part ( 12 ) has a surface ( 13 ), which is inclined and is embodied as oval, which is disposed opposite a magnetic field sensitive element ( 15 ) with an air gap (L 1 ). When there is movement, the air gap (L 1 ) changes so that the magnetic field sensitive element ( 15 ) generates an output signal proportional or linear to the movement direction R of the component to be monitored.

PRIOR ART

The invention is based on a measuring instrument. DE 29 23 644 C2 hasdisclosed a sensor for travel measurement which has a cylindricallyembodied frame made of a ferromagnetic material. A permanent magnet ismoved in a sliding fashion in the frame and its movement is transmittedwith the aid of a tappet and is proportional to the movement of acomponent. Furthermore, a magnetic field sensitive element is disposedin a gap in the frame and is consequently enclosed in the magneticcircuit produced by the magnet and its output signal is proportional tothe movement of the magnet. But the sensor is relatively complex andexpensive. Furthermore, a high friction losses can be produced with themovement of the magnet, which can distort the output signal.

SUMMARY OF THE INVENTION

The measuring instrument according to the invention, has the advantageover the prior art that for a low assembly cost, a linear output signalcan be determined for travel measurements. The distance to be determinedis relatively long and can, for example, be 10 mm. In addition, becauseof its simple construction, the sensor can be incorporated withoutexcessive alteration and assembly costs into systems such as an exhaustgas recirculation valve, valve stroke detection, body spring deflection,or transmission control.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are shown in the drawings andwill be explained in the description that follows.

FIG. 1 is a longitudinal section through a sensor,

FIG. 1a is a top view,

FIG. 1b is a view of the front end,

FIGS. 2 to 4 b respectively show modifications in the same views shownin FIGS. 1 to 1 b,

FIG. 5 is a section through an injection nozzle for supplying fuel in amotor vehicle with an internal combustion engine in which the stroke ofthe nozzle needle is to be detected.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a sensor 10 used to measure the travel of a component thatis not shown. The sensor 10 is comprised of a magnet 11, in particular apermanent magnet, which is polarized in the movement direction R, and aflux conducting part 12 made of magnetically conductive material, forexample soft iron. The flux conducting part 12 has a surface 13 that isinclined by an angle α in relation to the movement direction R.Furthermore, the flux conducting part 12 is manufactured in the form ofa cylinder, i.e. it has a circular cross section at the transition ofthe magnet 11 to the flux conducting part 12. Because of the virtuallycylindrical embodiment of the flux part 12, the surface 13 is embodiedas oval, as particularly shown in FIG. 1a. A magnetic field sensitiveelement 15 is disposed opposite the inclined surface 13 with an air gapL1. For example, magnetic field controlled photoresistance cells, magnettransistors, coils, magnetoresistive elements, or a Hall element can beused as magnetic field sensitive elements 15. It is important in thisconnection that the magnetic field sensitive element have as linear aspossible a dependency of its output signal on the magnetic induction B.As shown in FIG. 1b, the magnet 11 can also be embodied as cylindrical,and can have the same diameter as the flux conducting part 12. Dependingon the strength of the magnet and the required magnetic field that isused for the measurement, the magnet 11 a can also have a smallerdiameter than the flux conducting part 12. As shown in FIG. 3b, it isalso not necessary that the magnet 11 be the same shape as the fluxconducting part 12. For example, it can also have a quadriform crosssection, as shown in FIG. 3b or a rectangular cross section. In the fluxconducting part 12, however, it is necessary that the surface 13 have anoval form in order to obtain as linear an output signal as possible.

As shown in FIG. 4, it is not absolutely necessary that the inclinedsurface 13 begin directly at the transition from the magnet 11 to theflux conducting part 12. As shown in FIG. 4, a collar 20 can also bedisposed here before the inclined surface 13 begins. During the movementof the magnet 11 and the flux conducting part 12, which occurs parallelto the component to be measured in the movement direction R, the air gapL1 is enlarged or reduced depending on the movement direction. Themagnetic field sensitive element 15 is affixed in a stationary fashionso that the movement of the magnet 11 and the flux conducting part 12causes the air gap to change due to the inclined surface 13. Because thesize of the air gap L1 changes proportionally to the movement directionR, the magnetic field flowing through the magnetic field sensitiveelement 15 also changes so that the magnetic induction B produced in theelement 15 is changed.

FIG. 5 shows a section through an injection nozzle 21 for the meteredsupply of fuel to an internal combustion engine, for example a dieselengine. As a mechanical part, a nozzle needle 22, whose function is notexplained in detail here, executes partial, relatively short strokemovements in its longitudinal axis in order to open or close a valveseat in the injection nozzle 21. The end 23 of the nozzle needle 22protrudes through the stop shoulder of the spring of the nozzle needle22 and is connected to the magnet 11 of the sensor 10 there. Thelongitudinal axis of the nozzle needle 22 is aligned in the movementdirection R. The inclined surface 13 of the flux conducting part 12 isassociated with the stationarily disposed magnetic field sensitiveelement 15. The element 15 is connected with lines 25 to an electricunit 26 which is disposed in the housing of the injection nozzle 21.

What is claimed is:
 1. A travel measuring instrument, comprising a fluxconducting part composed of magnetically conductive material; a magnetpolarized in a movement direction; a magnetic field sensitive element,said flux conducting part having an inclined surface which isoperationally connected to said magnetic field sensitive element, saidinclined surface of said flux conducting part being substantially oval,and said magnetic field sensitive element and said inclined surfacebeing formed so that a relative motion occurs between said magneticfield element and said inclined surface.
 2. A travel measuringinstrument as defined in claim 1, wherein said magnetic field sensitiveelement is located substantially parallel to said inclined surface.
 3. Atravel measuring instrument as defined in claim 1, wherein said magneticfield sensitive element is a Hall element.
 4. A travel measuringinstrument as defined in claim 1, wherein said flux conducting part hasa round cross-section at least at a transition to said magnet.
 5. Atravel measuring instrument comprising a flux conducting part composedof magnetically conductive material; a magnet disposed on one end ofsaid flux conducting part; a magnetic field sensitive element, said fluxconducting part having a surface which is inclined in relation to amovement direction and is operationally connected to said magnetic fieldsensitive element, said magnetic field sensitive element and saidinclined surface being formed so that a relative motion occurs betweensaid magnet field sensitive element and said inclined surface, saidmagnetic being polarized in the movement direction and said inclinedsurface of said flux conducting part being substantially oval.